The correct answer is Clustered storage.

Clustered storage describes linking multiple storage servers so they operate as a single system to increase throughput capacity and resilience. Clustered storage implementations pool capacity and distribute data and metadata across nodes so clients see a unified storage service and the cluster can provide scalability and failover.

Software defined storage is an architectural approach that separates storage control from hardware and applies policy and automation across pooled resources. Software defined storage can enable clustered solutions but the term refers to the management model rather than the specific pattern of linking servers to behave as one clustered system.

Distributed file system refers to presenting a shared file namespace across multiple machines and it emphasizes file access and replication. A distributed file system may span many nodes but the phrase does not specifically denote the pooled block or object storage cluster that is described by Clustered storage.

Storage area network is a network architecture that connects hosts to centralized storage over a dedicated fabric. Storage area network describes connectivity and storage networking rather than the practice of linking storage servers themselves to form a single resilient and high throughput storage system.

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